support `top` and `primary` as role param in configuration

If `role` is set to `top` the location marker is displayed on top. This is a naive/manual solution to the marker overlap problem for adjacent timezones. cc. @abhayashenoy

![screen shot 2014-03-26 at 11 15 52 am](https://f.cloud.github.com/assets/412533/2520778/2242fb52-b495-11e3-8907-96175ca6a0e4.png)